1. Field of the Invention
The present invention relates to an electroluminescent (EL) device, and, more particularly, to a method of manufacturing an EL device which can simultaneously form various types of insulating layers on a substrate and on at least some portions of a first electrode.
2. Description of the Related Art
EL devices are self-emission type display devices, and much attention has recently been paid to the EL devices because they have advantageous features suitable for next generation devices, such as a wide viewing angle, a high contrast ratio, and a high response speed. EL devices are classified into inorganic EL devices and organic EL devices, according to the materials used in forming emission layers.
In particular, many studies of organic EL devices have been carried out because of their numerous advantages, including good characteristics in terms of brightness, response speed, color displaying, and so on.
An EL device is basically configured such that an anode is formed on a transparent insulating substrate, e.g., a glass substrate, in a predetermined pattern, a light emission layer consisting of organic or inorganic layers is formed on the anode, and a cathode having a predetermined pattern is then stacked thereon so as to be orthogonal with the anode.
The organic or inorganic layers have at least a light emission layer. As described above, the light emission layer is made of either an organic or inorganic material.
Usable materials of the organic layer include copper phthalocyanine (CuPc), N,N′-di(naphthalene-1-yl)- N,N′-diphenyl-benzidine (NPB), and tris-8-hydroxyquinoline aluminum (Alq3).
In the above-described EL device, when a drive voltage is applied to the anode and the cathode, holes from the anode migrate to the light emission layer, and electrons from the cathode migrate to the light emission layer. The holes and the electrons are recombined in the light emission layer to generate excitons. As the excitons are deactivated to a ground state, fluorescent molecules of the light emission layer emit light, thereby forming an image.
As described above, EL devices are classified into organic EL devices and inorganic EL devices according the materials used for light emission layers. An explanation will now be given by referring to an organic EL device.
In an organic EL device, an anode formed on the top surface of a substrate in a predetermined pattern is a transparent electrode, e.g., indium tin oxide (ITO), which is ordinarily formed by photolithography. Organic layers are formed on the anode by vacuum deposition and a cathode is then patterned thereon.
In the organic EL device having the above-described configuration, a high degree of precision is required in patterning the light emission layer of the organic layers, and patterning a cathode corresponding to an anode, and a variety of techniques have been proposed.
One of the typical methods of forming a cathode having a predetermined pattern is photolithography. If the cathode is formed by photolithography, however, there is a problem in that when the cathode is selectively etched using a photoresist, and the photoresist is stripped off or development is carried out, moisture may soak into an interface between organic layers and the cathode, resulting in degradation in electroluminescent performance due to the deteriorated characteristics of the organic layer, a low luminous efficiency, and a shortened life due to stripping of the cathode.
For overcoming those problems arising due to the entry of moisture, a new method using vacuum deposition, in which a deposition mask is employed, has been utilized to form organic layers or cathodes. However, it is quite difficult to form fine patterns on a large substrate using a deposition mask.
Recently known methods for solving the above-described problems include vacuum deposition using a cathode separator as disclosed in U.S. Pat. No. 5,701,055. According to this method using the shade of a separator, however, highly accurate patterning and high-speed deposition cannot be achieved under the conditions of variable deposition rates and a large amount of material deposited. Also, since portions where cathodes are not formed corresponding to the shade exist in organic layers, these portions are susceptible to ingress of moisture, resulting in deterioration of the organic layers. The deterioration of the organic layers may cause a short-circuit between the anodes and the cathodes.
In another method of forming cathodes, patterned cathodes are directly formed using a deposition mask. This method also has many problems. For example, the thin slit-shaped deposition mask may experience a sag of its central portion in a larger substrate, causing damage to organic layers or cathodes, thereby adversely affecting the yield. The sag also makes it impossible to form cathodes having finer patterns.
A known technique to solve the sag problem of a deposition mask includes disposing a magnetic medium at the opposite side of the deposition mask and closely contacting the deposition mask with an organic layer. However, close contact of the deposition mask may cause the organic layer to be damaged, resulting in a short-circuit between an anode and a cathode.
In order to prevent the damage of an organic layer due to a deposition mask, Japanese Patent Laid-Open Publication No. hei 10-241859 discloses an organic electroluminescent device having shielding walls with a predetermined height formed between the respective lines of an anode. However, according to this method, a gap between the anode and each of the shielding walls makes the organic layer formed at the edge of the anode thinner. Resultantly, the cathode may contact the anode at a lateral portion of the anode, causing a short-circuit between the cathode and the anode.
To prevent a short-circuit between electrodes, it is necessary to insulate non-pixel portions from each other. Also, in order to prevent organic layers from being damaged by a deposition mask, formation of insulating walls is necessary.
Separately, it is also necessary to form shielding walls for preventing an adhesive agent from infiltrating into the device. The adhesive agent is used during sealing of the device using a metal cap, which is performed after completing all film forming steps. The shielding walls should be formed outside the sealed portion of the device, as well as inside the device, as it is also sealed with the adhesive agent to prevent external terminals to be connected with a PCB from being contaminated.
Also, sealing portions for preventing moisture from infiltrating into the device through electrodes extending outward through the sealing portions should be formed using an insulating material having good moisture resistance.
To form such insulating members, photolithography can be employed, including coating a photosensitive resin material, exposing, and developing. However, in the case of using photolithography for forming the insulating members, different steps for forming insulating members having different heights should be separately performed, increasing the total number of processing steps and lowering processing efficiency and manufacturability.